Radio frequency remote control systems are used in a number of vehicle applications, such as various combinations of convenience and security systems. For example, remote starter and security systems feature a transmitter carried by a user and a receiver mounted in the vehicle to receive the transmitted signal in order to remotely start the vehicle. The skilled person will appreciate that some of the combinations of vehicle applications to be remotely controlled, while not exhaustively listed, could comprise for example a convenience system alone, a security system alone, or a combined convenience and security system.
Historically the radio frequency remote control systems have been using amplitude modulation (AM) schemes due to their lower manufacturing costs, compactness, and ease of implementation.
Radio frequency remote control systems for vehicle applications may have unidirectional or bidirectional communications capability. In a unidirectional system, the user can send wireless signals to the vehicle. In a bidirectional system, the user can send wireless signals to the vehicle, and the vehicle can respond with for example feedback signals to indicate changes of state in the vehicle's security status, or a confirmation that a particular command has been carried out. In a bidirectional system the vehicle can autonomously send signals to the user, for example to warn the user that the vehicle is being tampered with.
In a vehicle environment there are many potential sources of electrical interference (RF noise). The sources of RF noise can be from the vehicle itself or from external sources, especially in an urban environment. Furthermore, the characteristics of on-vehicle RF noise may change during the service life of a particular vehicle. For example, the electric motor that drives the heater blower emits electrical interference at a certain frequency in a new vehicle. As the blower ages and wears, the frequency of the electrical interference may change, thus placing an additional technical challenge on the remote control system to provide the expected range.
RF noise will reduce the range of an AM remote control system because the signal is encoded in the amplitude. The RF noise tends to affect the amplitude of an AM signal and will therefore change the information being carried, resulting in “interference”. So, while many radio frequency remote control systems for vehicle applications have been designed using AM receivers and transmitters, the AM solution is less resistant to interference.
Prior art remote control communications devices have been devised to attempt to address the problems cited above but the disadvantages remain.
For example, US2004/0037365: Remote transmitter system and method. An AM carrier signal of selectable frequency is applied, but still an AM signal with attendant drawbacks.
U.S. Pat. No. 4,660,192: Simultaneous AM and FM transmitter and receiver. This patent teaches simultaneous modulation of a carrier in AM and FM.
FM is more resistant to RF noise, however requires a more complex oscillator and receiver design. The reason why an FM signal is less affected by RF noise is because the FM signal has constant amplitude but varying frequency. The data is encoded by varying the frequency and thus RF noise does not affect FM as much.
It is an object of the present invention to provide a wireless remote control system with improved range and resistance to RF noise, for vehicle applications. Furthermore, the same solution could be applied to equivalent wireless remote control systems, regardless of the application, for stationary as well as mobile systems.
It is a further object of the present invention to carry out mode optimization when data is exchanged between a remote and a mobile.
It is another object of the present invention to carry out mode synchronization so a remote control system is continuously ready for service.
It is yet another object of the present invention to notify the user if the remote unit is out of range of the mobile unit.